Human opsonic protein concentrated in plasma cryoprecipitate has been shown recently to be effective in the treatment of septic shock. The overall goal of the proposed research is to utilize microcarrier-grown human cell cultures, especially fibroblasts, for the production and subsequent purification of opsonic protein (i.e., alpha-2-surface-binding glycoprotein or fibronectin). The investigation will involve screening a number of human cell types for their ability to produce opsonic protein, exploring the influence of cells age and cell cycle on this process, and optimization of environmental conditions (e.g., microcarrier density, bead charge, nutrients etc.) to obtain the maximum yield of protein. Postculture purification of the opsonic protein will be attempted by combination of ammonium sulfate fractionation, binding and release from insolubilized fibrinogen, density gradient electrophoresis, and recycling gel filtration on Sepharose 4B. In vitro opsonic activity will be demonstrated by standard procedures. In vivo testing will be performed with experimentally induced septic shock in baboons. Opsonic protein produced by such procedures may be used advantageously both from economic, biological, and immunological considerations over plasma cryoprecipitate infusion.